Memory element and memory device

ABSTRACT

There is disclosed a memory element including a memory layer that maintains information through the magnetization state of a magnetic material, a magnetization-fixed layer with a magnetization that is a reference of information stored in the memory layer, and an intermediate layer that is formed of a non-magnetic material and is provided between the memory layer and the magnetization-fixed layer. The storing of the information is performed by inverting the magnetization of the memory layer by using a spin torque magnetization inversion occurring according to a current flowing in the lamination direction of a layered structure having the memory layer, the intermediate layer, and the magnetization-fixed layer, the memory layer includes an alloy region containing at least one of Fe and Co, and a magnitude of an effective diamagnetic field which the memory layer receives during magnetization inversion thereof is smaller than the saturated magnetization amount of the memory layer.

CROSS REFERENCES TO RELATED APPLICATIONS

The present application claims priority to Japanese Priority PatentApplication JP 2010-196418 filed in the Japan Patent Office on Sep. 2,2010, the entire contents of which are hereby incorporated by reference.

BACKGROUND

The present disclosure relates to a memory element and a memory devicethat have a plurality of magnetic layers and make a record using a spintorque magnetization inversion.

Along with a rapid development of various information apparatuses frommobile terminals to large capacity servers, further high performanceimprovements such as higher integration, increases in a speed, and lowerpower consumption have been pursued in elements such as a memory elementand a logic element. Particularly, semiconductor non-volatile memory hassignificantly progressed, and, as a large capacity file memory, flashmemory has been spreading, and driving out had disk drives withmomentum. Meanwhile, looking at development of code storage or workingmemory, the development of FeRAM (Ferroelectric Random Access Memory),MRAM (Magnetic Random Access Memory), PCRAM (Phase-Change Random AccessMemory), or the like has progressed as a substitute for the current NORflash memory, DRAM or the like in general use. A part of these isalready practical in use.

Among them, the MRAM performs the data storage using the magnetizationdirection of a magnetic body, such that high speed and nearly unlimited(1015 times or more) rewriting can be made, and therefore the MRAMalready has been used in fields such as industrial automation and anairplane. Due to high-speed operation and reliability, the MRAM has beenexpected to be expanded to code storage or working memory in the nearfuture, but in practice, has challenges related to lowering powerconsumption and increasing capacity. This is a basic problem caused bythe recording principle of MRAM, that is, the method of reversing themagnetization using a current magnetic field generated from aninterconnect.

As a method of solving this problem, a recording method not utilizingthe current magnetic field, that is, a magnetization inversion method isunder review. Particularly, research on a spin torque magnetizationinversion has been actively made (for example, refer to JapaneseUnexamined Patent Application Publication Nos. 2003-17782 and2008-227388, a specification of U.S. Pat. No. 6,256,223, Phys. Rev. B,54, 9353 (1996), and J. Magn. Mat., 159, L1 (1996)).

The memory element of a spin torque magnetization inversion isfrequently configured using a MTJ (Magnetic Tunnel Junction) in the sameway as MRAM.

This configuration uses a phenomenon when spin-polarized electronspassing through a magnetic layer which is fixed in an arbitrarydirection enter another free (the direction is not fixed) magneticlayer, the spin-polarized electrons apply a torque to the free magneticlayer (this is also called a spin transfer torque), and when a currentof an arbitrary threshold or more flows, the free magnetic layer isinverted. The rewriting of 0/1 is performed by changing the polarity ofthe current.

An absolute value of a current for this inversion is 1 mA or less in thecase of an element with a scale of approximately 0.1 μm. In addition,this current value decreases in proportion to an element volume, suchthat scaling is possible. In addition, a word line necessary for thegeneration of a recording current magnetic field in the MRAM is notnecessary, such that there is an advantage in that a cell structurebecomes simple.

Hereinafter, the MRAM utilizing spin torque magnetization inversion isreferred to as an ST-MRAM (Spin Torque-Magnetic Random Access Memory).Spin torque magnetization inversion may be referred to as a spininjection magnetization inversion. Great expectations are put on theST-MRAM as a non-volatile memory capable of realizing lowerpower-consumption and larger capacity while maintaining the merits ofthe MRAM in that high speed and nearly unlimited rewriting may beperformed.

FIGS. 6 and 7 show schematic diagrams of the ST-MRAM. FIG. 6 is aperspective view and FIG. 7 is a cross-sectional view.

A drain region 58, a source region 57, and a gate electrode 51 that makeup a selection transistor for the selection of each memory cell areformed, respectively, in a semiconductor substrate 60, such as a siliconsubstrate, at portions isolated by an element isolation layer 52. Amongthem, the gate electrode 51 also functions as a word line extending inthe front-back direction in FIG. 7.

The drain region 58 is formed commonly to left and right selectiontransistors in FIG. 7, and an interconnect 59 is connected to the drainregion 58.

A memory element 53 having a memory layer in which a magnetizationdirection is inverted by spin torque magnetization inversion is disposedbetween the source region 57 and bit lines 56 that are disposed at anupper side and extend in the left-right direction in FIG. 6.

This memory element 53 is configured by, for example, a magnetic tunneljunction element (MTJ element). The memory element 53 has two magneticlayers 61 and 62. In the two magnetic layers 61 and 62, one sidemagnetic layer is set as a magnetization-fixed layer in which themagnetization direction is fixed, and the other side magnetic layer isset as a magnetization-free layer in which that magnetization directionvaries, that is, a memory layer.

In addition, the memory element 53 is connected to each bit line 56 andthe source region 57 through the upper and lower contact layers 54,respectively. In this manner, when a current is made to flow to thememory element 53, the magnetization direction of the memory layer maybe inverted by spin injection.

SUMMARY

However, in the case of the MRAM, a write interconnect (word line or bitline) is provided separately from the memory element, and the writing ofinformation (recording) is performed by a current magnetic fieldgenerated by flowing a current to the write interconnect. Therefore, itis possible to make a sufficient amount of current necessary for thewriting flow to the write interconnect.

On the other hand, in regard to the ST-MRAM, it is necessary to invertthe magnetization direction of the memory layer by performing spintorque magnetization inversion through a current flowing to the memoryelement.

Since the writing (recording) of information is performed by directlyflowing a current to the memory element as described above, a memorycell is configured by connecting the memory element to a selectiontransistor to select a memory cell that performs the writing. In thiscase, the current that flows to the memory element is restricted to acurrent magnitude capable of flowing to the selection transistor (asaturation current of the selection transistor).

Therefore, it is necessary to perform writing with a current equal to orless than the saturation current of the selection transistor, and it isknown that the saturation current of the transistor decreases along withminiaturization, such that for miniaturization of the ST-MRAM, it isnecessary to diminish the current flowing to the memory element byimproving spin transfer efficiency.

In addition, increase read-out signal strength, it is necessary tosecure a large magnetoresistance change ratio, and to realize this, itis effective to adopt the above-described MTJ structure, that is, toconfigure the memory element in such a manner that an intermediate layerconnected to both sides of the memory layer is set to as a tunnelinsulating layer (tunnel barrier layer).

In a case where the tunnel insulating layer is used as the intermediatelayer, the amount of current flowing to the memory element is restrictedto prevent the insulation breakdown of the tunnel insulating layer. Thatis, it is necessary to restrict the current necessary for the spintorque magnetization inversion in a viewpoint of securing reliabilitywith respect to a repetitive writing of the memory element.

Since such a current value is proportional to a film thickness of thememory layer and is proportional to the square of the saturationmagnetization of the memory layer, it may be effective to adjust these(the film thickness or the saturated magnetization) to decrease such acurrent value (for example, refer to Appl. Phys. Lett., 77, 3809 (2000).

For example, in a specification of U.S. Pat. No. 7,242,045, the factthat when the amount of magnetization (Ms) of the recording material isdecreased, the current value may be diminished is disclosed.

However, on the other hand, since the ST-MRAM is a non-volatile memory,it is necessary to stably store such information written by a current.That is, it is necessary to secure stability (thermal stability) withrespect to thermal fluctuations in the magnetization of the memorylayer.

In addition, in a case where the thermal stability of the memory layeris not secured, an inverted magnetization direction may be re-inverteddue to heat (temperature in an operational environment), and result in awriting error.

The memory element in the ST-MRAM is advantageous in scaling compared tothe MRAM in the related art, that is, advantageous in that the volume ofthe memory layer may be small as described above from the viewpoint ofthe recording current value. However, as the volume is small, thethermal stability may be deteriorated as long as other characteristicsare the same.

Therefore, the capacity increase of the ST-MRAM proceeds, the volume ofthe memory element becomes smaller, such that it is important to securethe thermal stability.

Therefore, in regard to the memory element of the ST-MRAM, the thermalstability is a significantly important characteristic, and it isnecessary to design the memory element in such a manner that the thermalstability thereof is secured even when the volume is diminished.

That is, to realize the ST-MRAM as a not-volatile memory, it isnecessary to decrease the current necessary for spin torquemagnetization inversion to a current equal to or less than a saturationcurrent of the transistor or to a current equal to or less than thecurrent at which a tunnel barrier is broken, and further it is necessaryto secure the thermal stability for maintaining recorded information.

As described above, to diminish the current necessary for spin torquemagnetization inversion, a method of diminishing the saturatedmagnetization amount Ms of the memory layer or a method of making thememory layer thin is considered. For example, as described in aspecification of U.S. Pat. No. 7,242,045, it is effective to use amaterial having a low saturated magnetization amount Ms as a material ofthe memory layer.

However, as described above, in the case of simply using the materialhaving a low saturated magnetization amount Ms, it is difficult tosecure the thermal stability for maintaining the information.

Therefore, it is desirable to provide a memory element capable ofimproving thermal stability without increasing the write current, and amemory device including the memory element.

According to an embodiment, there is provided a memory element includinga memory layer that maintains information through the magnetizationstate of a magnetic material; a magnetization-fixed layer withmagnetization that is a reference of information stored in the memorylayer; and an intermediate layer that is formed of a non-magneticmaterial and is provided between the memory layer and themagnetization-fixed layer, wherein the storing of the information isperformed by inverting the magnetization of the memory layer by using aspin torque magnetization inversion that occurs according to a currentflowing in the lamination direction of a layered structure having thememory layer, the intermediate layer, and the magnetization-fixed layer.The memory layer includes an alloy region containing at least one ofiron (Fe) and cobalt (Co), and a magnitude of an effective diamagneticfield which the memory layer receives during magnetization inversionthereof is smaller than the saturated magnetization amount of the memorylayer.

In addition, the ferromagnetic material making up the memory layer mayinclude a Co—Fe alloy.

In addition, the memory layer may be formed of an alloy expressed byCo_(x)Fe_(100-x), and a direction of an easy axis of magnetization maybe perpendicular to a film face, here, x is atomic %, and 0≦x≦40.

In addition, the memory layer may be formed of an alloy expressed by(Co_(x)Fe_(100-x))M_(1-y), and a direction of an easy axis ofmagnetization may be perpendicular to a film face, here, M is an elementother than Fe and Co, x and y are atomic %, 0≦x≦40, and 0<y<100.

In addition, according to another embodiment, there is provided a memorydevice which includes a memory element that maintains informationthrough the magnetization state of a magnetic material; and two kinds ofinterconnects that intersect each other. The memory element include theabove-described memory element according to the embodiment, the memoryelement is disposed between the two kinds of interconnects, and acurrent flows to the memory element in the lamination direction throughthe two kinds of interconnects, and according to this, spin torquemagnetization inversion occurs.

According to the memory element of the embodiment, the memory layer thatmaintains information by the magnetization state of the magneticmaterial is provided, the intermediate layer is provided between thememory layer and the magnetization-fixed layer, and the storing of theinformation is performed by inverting the magnetization of the memorylayer by using a spin torque magnetization inversion that occursaccording to the current flowing in the lamination direction, such thatit is possible to perform the recording of the information by flowingthe current in the lamination direction. At this time, the magnitude ofthe effective diamagnetic field which the memory layer receives duringmagnetization inversion thereof is smaller than the saturatedmagnetization amount of the memory layer, such that the diamagneticfield which the memory layer receives becomes small, and it is possibleto diminish the write current value necessary for inverting themagnetization direction of the memory layer.

On the other hand, it is possible to diminish the amount of the writecurrent even when the saturated magnetization amount of the memory layeris not diminished, such that it is possible to secure the saturatedmagnetization amount necessary for maintaining sufficient thermalstability of the memory layer.

In addition, according to the configuration of the memory device of theembodiment, the current flows to the memory element in the laminateddirection through the two kinds of interconnects, and a spin transferoccurs, such that it is possible to perform the recording of informationby using a spin torque magnetization inversion by flowing the current inthe lamination direction through the two kinds of interconnects.

In addition, it is possible to diminish the amount of write current evenwhen the saturated magnetization amount of the memory layer isdiminished, such that the information recorded in the record element isstably maintained, and it is possible to realize miniaturization of therecord device, an increase in reliability, and low power-consumption.

According to the embodiments, it is possible to diminish the amount ofwrite current of the memory element even when the saturatedmagnetization amount of the memory layer is diminished, such that it ispossible to configure a memory element excellent in a characteristicbalance by sufficiently securing the thermal stability that is theinformation maintaining ability.

In this manner, it is possible to sufficiently obtain an operationmargin of the memory element by eliminating operation error.

Therefore, it is possible to realize a high reliability memory thatstably operates.

In addition, the write current is diminished, such that it is possibleto diminish power consumption during the writing into the memoryelement.

Therefore, it is possible to diminish power consumption of the entiretyof the memory device.

Additional features and advantages are described herein, and will beapparent from the following Detailed Description and the figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is an explanatory view illustrating a schematic configuration ofa memory according to an embodiment;

FIG. 2 is a cross-sectional view illustrating a memory element accordingthe embodiment;

FIG. 3 is a diagram illustrating a relationship between the amount of Coof a memory layer of 0.09×0.18 μm size and an inverted current density;

FIG. 4 is a diagram illustrating a relationship between the amount of Coof a memory layer of 0.09×0.18 μm size and an index of thermalstability;

FIG. 5 is a diagram illustrating a relationship between the amount of Coof a memory layer of 0.05×0.05 μm size and an index of thermalstability;

FIG. 6 is an explanatory view illustrating a schematic configuration ofa ST-MRAM; and

FIG. 7 is a cross-sectional view of the ST-MRAM of FIG. 6.

DETAILED DESCRIPTION

Embodiments of the present application will be described below in detailwith reference to the drawings.

1. Outline of Memory Element of Embodiment

2. Configuration of Embodiment

3. Experiment

1. Outline of Memory Element of Embodiment

First, an outline of a memory element of an embodiment according to thepresent application will be described.

The embodiment according to the present application performs therecording of information by inverting a magnetization direction of amemory layer of a memory element by the above-described spin torquemagnetization inversion.

The memory layer is formed of a magnetic material such as ferromagneticlayer, and maintains information through the magnetization state(magnetization direction) of the magnetic material.

The memory element has a layered structure shown as an example in FIG.2, and includes at least a memory layer 17 and a magnetization-fixedlayer 15 as two ferromagnetic layers, and an intermediate layer 16provided between the two magnetic layers.

The memory layer 17 has a magnetization perpendicular to a film face anda direction of the magnetization varies corresponding to information.

The magnetization-fixed layer 15 has a magnetization that is a referenceof information stored in the memory layer 17 and is perpendicular to thefilm face.

The intermediate layer 16 is formed of a non-magnetic material and isprovided between the memory layer 17 and the magnetization-fixed layer15.

A spin-polarized electron are injected in the lamination direction of alaminated structure having the memory layer 17, the intermediate layer16, and the magnetization-fixed layer 15, and the magnetizationdirection of the memory layer 17 is changed and thereby information isrecorded in the memory layer 17.

Here, the spin torque magnetization inversion will be briefly described.

The electrons have two kinds of spin angular momentums. These momentumsare defined as an upward direction and a downward direction. Both ofthem are the same in number at the inside of the non-magnetic material,and are different in number at the inside of the ferromagnetic material.In regard to the magnetization-fixed layer 15 and the memory layer 17that are two layers of ferromagnetic materials making up the ST-MRAM, acase will be considered where the electrons are made to move from themagnetization-fixed layer 15 to the memory layer 17 when a direction ofeach magnetic moment thereof is in a reverse direction state.

The magnetization-fixed layer 15 is a fixed magnetic layer in which adirection of a magnetic moment is fixed for a high coercive force.

The electrons passed through the magnetization-fixed layer 15 arespin-polarized, that is, the numbers facing upward and downward aredifferent from each other. When the thickness of the intermediate layer16 that is non-magnetic layer is made to be sufficiently thin, the spinpolarization is mitigated after the electrons passed themagnetization-fixed layer 15, and the electrons reach the other magneticmaterial, that is, the memory layer 17 before the electrons become anon-polarized state in a common non-polarized material (the numbersfacing upward and downward are the same).

In the memory layer 17, a symbol of the spin polarization is inverted,such that a part of the electrons is inverted for lowering the systemenergy, that is, the direction of the spin angular momentum isexchanged. At this time, the entire angular momentum of the system isnecessary to be maintained, such that a reaction equal to the totalangular momentum by the electron of which the direction is changed isapplied to a magnetic moment of the memory layer 17.

In a case where the current, that is, the number of electrons is small,the total number of electrons of which a direction is changed becomessmall, such that the change in the angular momentum occurring in themagnetic moment of the memory layer 17 becomes small, but when thecurrent is increased, it is possible to apply large change in theangular momentum within a unit time.

The change of the angular momentum with the passage of time is a torque,and when the torque exceeds a threshold value, the magnetic moment ofthe memory layer 17 starts a precession, and rotates 180° due touniaxial anisotropy thereof and becomes stable. That is, the inversionoccurs from the reverse direction state to the same direction state.

When the magnetization is the same direction state, if the current ismade to reversely flow from the memory layer 17 to themagnetization-fixed layer 15 in the direction of flowing the current,when the electrons that are spin-inverted at that time of beingreflected from the magnetic-fixed layer 15 enter the memory layer 17, atorque is applied, and it is possible to invert the magnetic moment tothe reverse direction state. However, at this time, the amount ofcurrent necessary for causing the inversion is larger than that in thecase of inverting from the reverse direction state to the same directionstate.

The inversion of the magnetic moment from the same direction state tothe reverse direction state is difficult to intuitively understand, butit may be considered that the magnetization-fixed layer 15 is fixed,such that the magnetic moment is not inverted, and the memory layer 17is inverted for maintaining the angular momentum of the entire system.As described above, the recording of 0/1 is performed by flowing acurrent of a certain threshold value or more, which corresponds to eachpolarity, from the magnetization-fixed layer 15 to the memory layer 17or in an reverse direction thereof.

A read-out of information is performed by using a magnetoresistiveeffect similarly to the MRAM in the related art. That is, as is the casewith the above-described recording, current is made to flow in adirection perpendicular to the film face. In addition, a phenomenon isused where an electrical resistance shown by an element varies accordingto whether the magnetic moment of the memory layer 17 is the samedirection or the reverse direction as the magnetic moment of themagnetization-fixed layer 15.

A material used for the intermediate layer 16 disposed between themagnetization-fixed layer 15 and the memory layer 17 may be a metallicmaterial or an insulating material, but the insulating material may beused for the intermediate layer to obtain a relatively high read-outsignal strength (resistance change ratio), and to realize the recordingby a relatively low current. The element at this time is called aferromagnetic tunnel junction (Magnetic Tunnel Junction: MTJ).

When the magnetization direction of the magnetic layer is inverted byspin torque magnetization inversion, a necessary threshold value Ic of acurrent is expressed by the following equation (1).Ic=A·α·Ms·V·Hd/2η  (1)

Here, A: constant, α: spin braking constant, η: spin injectionefficiency, Ms: saturated magnetization amount, V: volume of memorylayer, and Hd: effective diamagnetic field.

As expressed by the equation (1), a threshold value of a current may beset to an arbitrary value by controlling the volume V of the magneticlayer, the saturated magnetization Ms of the magnetic layer, and thespin injection efficiency η, and the spin braking constant α, and may beset to an arbitrary value.

In this embodiment, the memory element includes the magnetic layer(memory layer 17) that is capable of maintaining information through themagnetization state, and the magnetization-fixed layer 15 whosemagnetization direction is fixed.

The memory element has to maintain written information so as to functionas a memory. This is determined by a value of an index Δ (=KV/k_(B)T) ofthermal stability as an index of ability of maintaining information. Theabove-described Δ is expressed by the following equation (2).Δ=KV/k _(B) T=Ms·V·H _(k)·(½k _(B) T)  (2)

Here, H_(k): effective anisotropy field, k_(B): Boltzmann's constant, T:temperature, Ms: amount of saturated magnetism, and V: volume of memorylayer.

The effective anisotropy field H_(k) receives an effect by a shapemagnetic anisotropy, an induced magnetic anisotropy, and a crystalmagnetic anisotropy, or the like, and when assuming a coherent rotationmodel of a single domain, the effective anisotropy field becomes thesame as the coercive force.

The index Δ of the thermal stability and the threshold value Ic of thecurrent are often in a trade-off relationship. Therefore, compatibilitybecomes an issue in maintaining the memory characteristic.

In regard to the threshold value of the current that changes themagnetization state of the memory layer, actually, for example, in a TMRelement in which the thickness of the memory layer 17 is 2 nm, and aplanar pattern is substantially an elliptical shape of 100 nm×150 nm, athreshold value +Ic of a positive side is +0.5 mA, a threshold value −Icof a negative side is −0.3 mA, and a current density at this time issubstantially 3.5×106 A/cm2. These substantially correspond to theabove-described equation (1).

On the contrary, in a common MRAM that performs a magnetizationinversion by a current magnetic field, a write current of several mA ormore is necessary.

Therefore, in the case of the ST-MRAM, the threshold value of theabove-described write current becomes sufficiently small, such that thisis effective for diminishing the power consumption of an integratedcircuit.

In addition, an interconnect for the generation of the current magneticfield, which is necessary for a common MRAM, is not necessary, such thatin regard to the degree of integration, it is advantageous compared tothe common MRAM.

In the case of performing the spin torque magnetization inversion, sincethe writing (recording) of information is performed by directly flowinga current to the memory element, to select a memory cell that performsthe writing, the memory element is connected to a selection transistorto construct the memory cell.

In this case, the current flowing to the memory element is restricted tothe magnitude of a current (saturated current of the selectiontransistor) that can be made to flow to the selection transistor.

To make the threshold value Ic of a current of the magnetizationinversion by the injection of a spin smaller than the saturated currentof the selection transistor, as can be seen from the equation (1), it iseffective to diminish the saturated magnetization amount Ms of thememory layer 17.

However, in the case of simply diminishing the saturated magnetizationamount Ms (for example, U.S. Pat. No. 7,242,045), the thermal stabilityof the memory layer 17 is significantly deteriorated, and therefore itis difficult for the memory element to function as a memory.

To construct the memory, it is necessary that the index Δ of the thermalstability be equal to or greater than a magnitude of a certain degree.

The present inventors have made various studies, and as a resultthereof, they have found that when the ferromagnetic layer making up thememory layer 17 is formed of an alloy including cobalt (Co) and iron(Fe), and a composition of Co—Fe is selected, the magnitude of theeffective diamagnetic field (M_(effective)) which the memory layer 17receives becomes smaller than the saturated magnetization amount Ms ofthe memory layer 17.

By using the above-described ferromagnetic material, the magnitude ofthe effective diamagnetic field which the memory layer 17 receivesbecomes smaller than the saturated magnetization amount Ms of the memorylayer 17.

In this manner, it is possible to make the diamagnetic field which thememory layer 17 receives small, such that it is possible to obtain aneffect of diminishing the threshold value Ic of a current expressed bythe equation (1) without deteriorating the thermal stability Δ expressedby the equation (2).

In addition, the present inventors has found that Co—Fe magnetizes in adirection perpendicular to a film face within a restricted compositionrange of the selected Co—Fe composition, and due to this, it is possibleto secure a sufficient thermal stability even in the case of a extremelyminute recording element capable of realizing Gbit class capacity.

Therefore, in a state where the thermal stability is secured in theST-MRAM of Gbit class, it is possible to make a stable memory in whichinformation may be written with a low current.

In this embodiment, it is configured such that the magnitude of theeffective diamagnetic field which the memory layer 17 receives is madeto be less than the saturated magnetization amount Ms of the memorylayer 17, that is, a ratio of the magnitude of the effective diamagneticfield with respect to the saturated magnetization amount Ms of thememory layer 17 becomes less than 1.

In addition, a magnetic tunnel junction (MTJ) element is configured byusing a tunnel insulating layer formed of an insulating material as thenon-magnetic intermediate layer 16 disposed between the memory layer 17and the magnetization-fixed layer 15 in consideration of the saturatedcurrent value of the selection transistor.

The magnetic tunnel junction (MTJ) element is configured by using thetunnel insulating layer, such that it is possible to make amagnetoresistance change ratio (MR ratio) large compared to a case wherea giant magnetoresistive effect (GMR) element is configured by using anon-magnetic conductive layer, and therefore it is possible to makeread-out signal strength large.

Particularly, when magnesium oxide (MgO) is used as the material of theintermediate layer 16 as the tunnel insulating layer, it is possible tomake the magnetoresistance change ratio (MR ratio) large compared to acase where aluminum oxide, which can be generally used, is used.

In addition, generally, the spin transfer efficiency depends on the MRratio, and as the MR ratio is large, the spin transfer efficiency isimproved, and therefore it is possible to diminish the magnetizationinversion current density.

Therefore, when magnesium oxide is used as the material of the tunnelinsulating material and the memory layer 17 is used, it is possible todiminish the threshold write current by spin torque magnetizationinversion and therefore it is possible to perform the writing(recording) of information with a small current. In addition, it ispossible to make the read-out signal strength large.

In this manner, it is possible to diminish the writing threshold currentby spin torque magnetization inversion by securing the MR ratio (TMRratio), and it is possible to perform the writing (recording) ofinformation with a small current. In addition, it is possible to makethe read-out signal strength large.

As described above, in a case where the tunnel insulating layer isformed of the magnesium oxide (MgO) film, it is desirable that the MgOfilm is crystallized and therefore a crystal orientation is maintainedin (001) direction.

In addition, in this embodiment, in addition to a configuration formedof the magnesium oxide, the intermediate layer 16 (tunnel insulatinglayer) disposed between the memory layer 17 and the magnetization-fixedlayer 15 may be configured by using, for example, various insulatingmaterials, dielectric materials, and semiconductors such as aluminumoxide, aluminum nitride, SiO₂, Bi₂O₃, MgF₂, CaF, SrTiO₂, AlLaO₃, andAl—N—O.

An area resistance value of the tunnel insulating layer is necessary tobe controlled to several tens Ωμm² or less in consideration of theviewpoint of obtaining a current density necessary for inverting themagnetization direction of the memory layer 17 by spin torquemagnetization inversion.

In the tunnel insulating layer formed of the MgO film, to maintain thearea resistance value within the above-described range, it is necessaryto set the film thickness of the MgO film to 1.5 nm or less.

In addition, it is desirable to make the memory element small to easilyinvert the magnetization direction of the memory layer 17 with a smallcurrent.

Therefore, preferably, the area of the memory element is set to 0.01 μm2or less.

In addition, elements other than Co and Fe may be added to the memorylayer 17 as the embodiment.

When heterogeneous elements are added, there is obtained an effect suchas improvement in a heat resistance or increase in a magnetoresistiveeffect due to the prevention of diffusion, and increase in insulatingbreakdown voltage accompanied with planarization. As a material of thisadded element, B, C, N, O, F, Mg, Si, P, Ti, V, Cr, Mn, Ni, Cu, Ge, Nb,Mo, Ru, Rh, Pd, Ag, Ta, W, Ir, Pt, Au, Zr, Hf, Re, Os, or an alloythereof may be used.

In addition, as the memory layer 17 in this embodiment, a ferromagneticlayer with a different composition may be directly laminated. Inaddition, a ferromagnetic layer and a soft magnetic layer may belaminated, or a plurality of ferromagnetic layers may be laminatedthrough the soft magnetic layer or a non-magnetic layer. In the case oflaminating in this manner, it is possible to obtain an effect in thepresent application.

Particularly, in a case where the plurality of ferromagnetic layers arelaminated through the non-magnetic layer, it is possible to adjust thestrength interacting between the ferromagnetic layers, such that evenwhen the dimensions of the memory element is under sub-micron, there isobtained an effect of controlling magnetization inversion current not tobe large. As a material of the non-magnetic layer in this case, Ru, Os,Re, Ir, Au, Ag, Cu, Al, Bi, Si, B, C, Cr, Ta, Pd, Pt, Zr, Hf, W, Mo, Nb,or an alloy thereof may be used.

It is desirable that the magnetization-fixed layer 15 and the memorylayer 17 have a unidirectional anisotropy.

In addition, it is preferable that the film thickness of each of themagnetization-fixed layer 15 and the memory layer 17 be 0.5 to 30 nm.

Other configuration of the memory element may be the same as theconfiguration of a memory element that records information by spintorque magnetization inversion in the related art.

The magnetization-fixed layer 15 may be configured in such a manner thatthe magnetization direction is fixed by only a ferromagnetic layer or byusing an antiferromagnetic coupling of an antiferromagnetic layer and aferromagnetic layer.

In addition, the magnetization-fixed layer 15 may be configured by asingle layer of a ferromagnetic layer, or a ferri-pin structure in whicha plurality of ferromagnetic layers are laminated through a non-magneticlayer.

As a material of the ferromagnetic layer making up themagnetization-fixed layer 15 of the laminated ferri-pin structure, Co,CoFe, CoFeB, or the like may be used. In addition, as a material of thenon-magnetic layer, Ru, Re, Ir, Os, or the like may be used.

As a material of the antiferromagnetic layer, a magnetic material suchas an FeMn alloy, a PtMn alloy, a PtCrMn alloy, an NiMn alloy, an IrMnalloy, NiO, and Fe2O3 may be exemplified.

In addition, a magnetic characteristic may be adjusted by adding anon-magnetic element such as Ag, Cu, Au, Al, Si, Bi, Ta, B, C, O, N, Pd,Pt, Zr, Hf, Ir, W, Mo, and Nb to the above-describe magnetic materials,or in addition to this, various physical properties such as acrystalline structure, a crystalline property, a stability of asubstance, or the like may be adjusted.

In addition, in relation to a film configuration of the memory element,the memory layer 17 may be disposed at the lower side of themagnetization-fixed layer 15, or at the upper side thereof, and in anydisposition, there is no problem at all. In addition, there is noproblem at all in a case where the magnetization-fixed layer 15 isdisposed at the upper side and the lower side of the memory layer 17,so-called dual-structure.

In addition, as a method of reading-out information recorded in thememory layer 17 of the memory element, a magnetic layer that becomes areference of information is provided on the memory layer 17 of thememory element through a thin insulating film, and the reading-out maybe performed by a ferromagnetic tunnel current flowing through theinsulating layer (intermediate layer 16), or the reading-out may beperformed by a magnetoresistive effect.

2. Configuration of Embodiment

Subsequently, a specific configuration of this embodiment will bedescribed.

As an embodiment, a schematic configuration diagram (perspective view)of a memory device is shown in FIG. 1.

This memory device includes a memory element 3, which can maintaininformation at a magnetization state, disposed in the vicinity of anintersection of two kinds of address interconnects (for example, a wordline and a bit line) that are perpendicular to each other.

Specifically, a drain region 8, a source region 7, and a gate electrode1 that make up a selection transistor that selects each memory cell areformed in a portion separated by an element separation layer 2 of asemiconductor substrate 10 such as a silicon substrate, respectively.Among them, the gate electrode 1 also functions as one side addressinterconnect (for example, a word line) that extends in the front-backdirection in the drawing.

The drain region 8 is formed commonly with left and right selectiontransistors in the drawing, and an interconnect 9 is connected to thedrain region 8.

The memory element 3 is disposed between the source region 7, and theother side address interconnect (for example, a bit line) 6 that isdisposed at an upper side and extends in the left-right direction in thedrawing. This memory element 3 has a memory layer including aferromagentic layer whose magnetization direction is inverted by theinjection of a spin.

In addition, the memory element 3 is disposed in the vicinity of anintersection of two kinds of address interconnects 1 and 6.

The memory element 3 is connected to the bit line 6 and the sourceregion 7 through upper and lower contact layers 4, respectively.

In this manner, a current flows into the memory element 3 in theperpendicular direction thereof through the two kind of addressinterconnects 1 and 6, and the magnetization direction of the memorylayer may be inverted by a spin torque magnetization inversion.

In addition, a cross-sectional view of the memory element 3 of thememory device according to this embodiment is shown in FIG. 2.

As shown in FIG. 2, the memory element 3 has a magnetization-fixed layer15 provided at a lower layer in relation to a memory layer 17 in whichthe magnetization direction of a magnetization M17 is inverted by a spintorque magnetization inversion.

In regard to an ST-MRAM, 0 and 1 of information are defined by arelative angle between the magnetization M17 of the memory layer 17 anda magnetization M15 of the magnetization-fixed layer 15.

An intermediate layer 16 that serves as a tunnel barrier layer (tunnelinsulating layer) is provided between the memory layer 17 and themagnetization-fixed layer 15, and therefore an MTJ element is configuredby the memory layer 17 and the magnetization-fixed layer 15.

In addition, an underlying layer 14 is formed under themagnetization-fixed layer 15, and a cap layer 18 is formed on the memorylayer 17.

In this embodiment, particularly, a composition of the memory layer 17of the memory element 3 is adjusted such that a magnitude of aneffective diamagnetic field which the memory layer 17 receives becomessmaller than the saturated magnetization amount Ms of the memory layer17.

That is, as described above, a composition of a ferromagnetic materialCo—Fe of the memory layer 17 is selected, and the magnitude of theeffective diamagnetic field which the memory layer 17 receives is madeto be small, such that the magnitude of the effective diamagnetic fieldbecomes smaller than the saturated magnetization amount Ms.

In addition, in this embodiment, in a case where the intermediate layer16 is formed of a magnesium oxide layer, it is possible to make amagnetoresistive change ratio (MR ratio) high.

When the MR ratio is made to be high as described above, the spininjection efficiency is improved, and therefore it is possible todiminish the current density necessary for inverting the direction ofthe magnetization M17 of the memory layer 17.

The memory element 3 of this embodiment can be manufactured bycontinuously forming from the underlying layer 14 to the cap layer 18 ina vacuum apparatus, and then by forming a pattern of the memory element3 by a processing such as a subsequent etching or the like.

According to the above-described embodiment, the memory layer 17 of thememory element 3 is configured in such a manner that the magnitude ofthe effective diamagnetic field that the memory layer 17 receives issmaller than the saturated magnetization amount Ms of the memory layer17, such that the diamagnetic field that the memory layer 17 receives isdecreased, and it is possible to diminish the amount of write currentnecessary for inverting the direction of the magnetization M17 of thememory layer 17.

On the other hand, since the amount of write current may be diminishedeven when the saturated magnetization amount Ms of the memory layer 17is not diminished, it is possible to sufficiently secure the saturatedmagnetization amount of the memory layer 17 and therefore it is possibleto sufficiently secure the thermal stability of the memory layer 17.

As described above, since it is possible to sufficiently secure thethermal stability that is the information maintaining ability, it ispossible to configure the memory element 3 excellent in a characteristicbalance.

In this manner, an operation error is removed and an operation margin ofthe memory element 3 is sufficiently obtained, such that it is possibleto stably operate the memory element 3.

Accordingly, it is possible to realize a memory that stably operateswith high reliability.

In addition, the write current is diminished, such that it is possibleto diminish the power consumption when performing the writing into thememory element 3.

Therefore, it is possible to diminish the power consumption of theentirety of the memory in which a memory cell is configured by thememory element 3 of this embodiment.

Therefore, in regard to the memory including the memory element 3capable of realizing a memory that is excellent in the informationmaintaining ability, has high reliability, and operates stably, it ispossible to diminish the power consumption.

In addition, the memory that includes a memory element 3 shown in FIG. 2and has a configuration shown in FIG. 1 has an advantage in that ageneral semiconductor MOS forming process may be applied when the memoryis manufactured.

Therefore, it is possible to apply the memory of this embodiment as ageneral purpose memory.

3. Experiment

Here, in regard to the configuration of the memory element 3 of thisembodiment, by specifically selecting the material of the ferromagneticlayer making up the memory layer 17, the magnitude of the effectivediamagnetic field that the memory layer 17 receives was adjusted, andthereby a sample of the memory element 3 was manufactured, and thencharacteristics thereof was examined.

In an actual memory device, as shown in FIG. 1, a semiconductor circuitfor switching or the like present in addition to the memory element 3,but here, the examination was made on a wafer in which only the memoryelement is formed for the purpose of investigating the magnetizationinversion characteristic of the memory layer 17.

Experiment 1

A thermal oxide film having a thickness of 300 nm was formed on asilicon substrate having a thickness of 0.725 mm, and the memory element3 having a configuration shown in FIG. 2 was formed on the thermal oxidefilm.

Specifically, in regard to the memory element 3 shown in FIG. 1, amaterial and a film thickness of each layer were selected as describedbelow.

-   -   Underlying layer 14: Laminated film of a Ta film having a film        thickness of 10 nm and a Ru film having a film thickness of 25        nm    -   Magnetization-fixed layer 15: CoFeB film having a film thickness        of 2.5 nm    -   Intermediate layer (tunnel insulating layer) 16: Magnesium oxide        film having a film thickness of 0.9 nm    -   Memory layer 17: CoFe film    -   Cap layer 18: Laminated film of a Ta film having a film        thickness of 3 nm, a Ru film having a thickness of 3 nm, and a        Ta film having a thickness of 3 nm

Each layer was selected as described above, a Cu film (not shown) havinga film thickness of 100 nm (serving as a word line described below) wasprovided between the underlying layer 14 and the silicon substrate.

In the above-described configuration, the ferromagnetic layer of thememory layer 17 was formed of a binary alloy of Co—Fe, and a filmthickness of the ferromagnetic layer was fixed to 2.0 nm.

Each layer other than the intermediate layer 16 formed of a magnesiumoxide film was formed using a DC magnetron sputtering method.

The intermediate layer 16 formed of the magnesium oxide (MgO) film wasformed using a RF magnetron sputtering method.

In addition, after forming each layer of the memory element 3, a heatingtreatment was performed in a magnetic field heat treatment furnace.

Next, after masking a word line portion by a photolithography, aselective etching by Ar plasma was performed with respect to a laminatedfilm other than the word line portion, and thereby the word line (lowerelectrode) was formed. At this time, a portion other than the word linewas etched to the depth of 5 nm in the substrate.

Then, a mask of a pattern of the memory element 3 by an electron beamdrawing apparatus was formed, a selective etching was performed withrespect to the laminated film, and thereby the memory element 3 wasformed. A portion other than the memory element 3 was etched to aportion of the word line immediately over the Cu layer.

In addition, in the memory device for the characteristic evaluation, itis necessary to make a sufficient current flow to the memory element soas to generate a spin torque necessary for the magnetization inversion,such that it is necessary to suppress the resistance value of the tunnelinsulating layer. Therefore, a pattern of the memory element 3 was setto an elliptical shape having a short axis of 0.09 μm×a long axis of0.18 μm, and an area resistance value (Ωμm²) of the memory element 3 wasset to 20 Ωμm².

Next, a portion other than the memory element 3 was insulated bysputtering Al₂O₃ to have a thickness of substantially 100 nm.

Then, a bit line serving as an upper electrode and a measurement padwere formed by using photolithography.

In this manner, a sample of the memory element 3 was manufactured.

By the above-described manufacturing method, each sample of the memoryelement 3 in which a composition of Co—Fe alloy of the ferromagneticlayer of the memory layer 17 was changed was manufactured.

In the composition of the Co—Fe alloy, a Co composition ratio of Co inCoFe, that is, x (atomic %) was changed to 90%, 80%, 70%, 60%, 50%, 40%,30%, 20%, 10%, and 0%.

With respect to each sample of the memory element 3 manufactured asdescribed above, a characteristic evaluation was performed as describedbelow.

Before the measurement, it was configured to apply a magnetic field tothe memory element 3 from the outside to control an inversion current insuch a manner that a value in a plus direction and a value in a minusdirection to be symmetric to each other. In addition, a voltage appliedto the memory element 3 was set up to 1 V within a range withoutbreaking down the insulating layer (intermediate layer 16).

Measurement of Saturated Magnetization Amount

The saturated magnetization amount Ms was measured by a VSM measurementusing a Vibrating Sample Magnetometer.

Measurement of Effective Diamagnetic Field

As a sample for measuring an effective diamagnetic field, in addition tothe above-described sample of the memory element 3, a sample in whicheach layer making up the memory element 3 was formed was manufacturedand then the sample was processed to have a planar pattern of 20 mm×20mm square.

In addition, a magnitude M_(effective) an effective diamagnetic fieldwas obtained by FMR (Ferromagnetic Resonance) measurement.

A resonance frequency fFMR, which is obtained by the FMR measurement,with respect to arbitrary external magnetic field H_(ex) is given by thefollowing equation (3).f _(FMR)=γ′√{square root over (4πM _(effective)(H _(K) +H _(ex)))}  (3)

Here, M_(effective) in the equation (3) may be expressed by4πM_(effective)=4πMs−H⊥ (H⊥: anisotropy field in a directionperpendicular to a film face).

Measurement of Inversion Current Value and Thermal Stability

An inversion current value was measured for the purpose of evaluatingthe writing characteristic of the memory element 3 according to thisembodiment.

A current having a pulse width of 10 μs to 100 ms is made to flow to thememory element 3, and then a resistance value of the memory element 3was measured. In addition, the amount of current that flows to thememory element 3 was changed, and then a current value in which adirection of the magnetization M1 of the memory layer 17 of the memoryelement 3 was inverted was obtained. A value obtained by extrapolating apulse width dependency of this current value to a pulse width 1 ns wasset to the inversion current value.

In addition, the inclination of a pulse width dependency of theinversion current value corresponds to the above-described index Δ ofthe thermal stability of the memory element 3. The less the inversioncurrent value is changed (the inclination is small) by the pulse width,the more the memory element 3 is strong against disturbance of the heat.

In addition, twenty memory elements 3 with the same configuration weremanufactured to take variation in the memory element 3 itself intoconsideration, the above-described measurement was performed, and anaverage value of the inversion current value and the index Δ of thethermal stability were obtained.

In addition, an inversion current density Jc0 was calculated from theaverage value of the inversion current value obtained by the measurementand an area of the planar pattern of the memory element 3.

In regard to each sample of the memory element 3, a composition of Co—Fealloy of the storage layer 17, measurement results of the saturatedmagnetization amount Ms and the magnitude M_(effective) of the effectivediamagnetic field, and a ratio M_(effective)/Ms of effective diamagneticfield to the saturated magnetization amount were shown in Table 1. Here,the amount of Co of Co—Fe alloy of the memory layer 17 described inTable 1 was expressed by an atomic %.

TABLE 1 Ms[emu/cc] Meffective[emu/cc] Meffective/Ms Co90Fe10 1250 15001.2 Co80Fe20 1410 1440 1.02 Co70Fe30 1760 1510 0.86 Co60Fe40 1820 14400.79 Co50Fe50 1880 1260 0.67 Co40Fe60 1890 1100 0.58 Co30Fe70 1970 10600.54 Co20Fe80 1900 950 0.5 Co10Fe90 1830 975 0.53 Fe 1750 990 0.57

From the table 1, in a case where the amount x of Co of CO_(x)Fe_(100-x)is 70% or less, the magnitude of the effective diamagnetic field issmaller than the saturated magnetization amount Ms, that is, the ratioof M_(effective)/Ms in a case where the amount x of Co is 70% or lessbecomes a value less than 1.0.

In addition, until the amount x of Co becomes 20%, as the amount x of Codecreases, the value of M_(effective)/Ms decreases, but it was confirmedthat when the amount x of Co further decreases, the ratio increases alittle.

A measurement result of the inversion current value was shown in FIG. 3,and a measurement result of the index of the thermal stability was shownin FIG. 4.

FIG. 3 shows a relationship between the amount x (content in CoFe;atomic %) of Co in the Co—Fe alloy of the memory layer 17 and theinversion current density Jc0 obtained from the inversion current value.

FIG. 4 shows a relationship between the amount x (content in CoFe;atomic %) of Co in the Co—Fe alloy of the memory layer 17 and the indexΔ (kV/k_(B)T) of the thermal stability.

As can be seen from FIG. 3, in a case where the amount x of Co is 70% orless, as the amount x of Co decreases, the inversion current density Jc0decreases.

This is because in a case where the amount x of Co becomes small, thesaturated magnetization amount Ms increases, but the effectivediamagnetic field M_(effective) decreases, and therefore the product ofthem Ms×M_(effective) becomes small.

As can be seen from FIG. 4, as the amount x of Co decreases, the index Δ(KV/k_(B)T) of the thermal stability increases, and in a case where theamount x of Co is 70% or less, the index Δ of the thermal stabilitybecomes stable to a large value.

This well corresponds to a change that is expected from the measurementresult of the saturated magnetization amount Ms shown in Table 1 and atendency where the index Δ of the thermal stability from the equation(2) is proportional to the saturated magnetization amount Ms.

As is clear from the results of Table 1, FIGS. 3 and 4, in a compositionwhere the amount x of Co is 70% or less and the effective diamagneticfield M_(effective) is less than the saturated magnetization amount Ms,it is possible to diminish the inversion current value Jc0 with a highthermal stability maintained, without using a method in which Ms isdecreased and therefore the thermal stability is sacrificed.

Experiment 2

As can be seen from the above-described experiment 1, in the case ofCo_(x)Fe_(100-x), it is possible to diminish the inversion current valueJc0 with a high thermal stability maintained in a composition where theamount x of Co is 70% or less.

Therefore, in an experiment 2, B (boron) was added to the Co—Fe alloy toinvestigate an addition effect a heterogeneous element, and an effect onthe M_(effective)/Ms, which is caused by B, was examined by using amemory layer 17 having a composition (Co₅₀Fe₅₀)₉₂B₈. The details of thesample were substantially the same as those in the experiment 1.

As a result thereof, in regard to (Co₅₀Fe₅₀)₉₂B₈, values of thesaturated magnetization amount Ms and the magnitude M_(effective) of theeffective diamagnetic field were 1550 (emu/cc) and 950 (emu/cc),respectively, and a value of a ratio M_(effective)/MS of the magnitudeof the effective diamagnetic field to the saturated magnetization amountMs was 0.61.

That is, it was clear from the result that even when 8 atomic % of boronwas added, the relationship of the saturated magnetization amount Ms andthe magnitude of the effective diamagnetic field M_(effective) wasdetermined by a ratio of Co and Fe.

Therefore, it was considered that the configuration where the saturatedmagnetization amount Ms of the memory layer 17 was made to be smallerthan the effective diamagnetic field M_(effective) was not hindered bythe addition of the heterogeneous element. That is, an additive elementsuch as boron may be added for the purpose of generating a high tunnelmagnetoresistive effect, for the purpose of increasing an insulatingbreak-down voltage through the planarization of an interface, or thelike.

Experiment 3

In a spin injection type memory of a Gbit class, it was assumed that thesize of the recording element was 100 nmφ or less. Here, in anexperiment 3, the thermal stability was evaluated by using a memoryelement having a size of 50 nmφ.

In the composition of Co—Fe alloy, a composition ratio x (atomic %) inCoFe was changed to 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, 10%, and 0%,respectively. The details of a sample other than the element size weresubstantially the same as those in the experiment 1.

In a case where the size of the memory element 3 was 50 nmφ, arelationship between the amount of Co (content in CoFe; atomic %) in theCo—Fe alloy, and the index Δ (KV/k_(B)T) of the thermal stability wereshown in FIG. 5.

As can be seen from FIG. 5, when the element size was 50 nmφ, Co—Fealloy composition dependency of the thermal stability index Δ waslargely varied from the Co—Fe alloy composition dependency of Δ obtainedin the elliptical memory element having a short axis of 0.09×a long axisof 0.18 μm shown in FIG. 4.

According to FIG. 5, the high thermal stability was maintained only inthe case of Co—Fe alloy composition where Co is 40% or less, that is, Feis 60% or more.

As a result of various reviews, it was clear the reason why the Co—Fealloy containing Fe of 60% or more shown the high thermal stability Δ inthe extremely minute memory element was revealed to be because themagnetization of the Co—Fe alloy faced a direction perpendicular to afilm face (the direction in which the magnetization becomes stable in acase where the external magnetic field was not present is referred to as“easy axis direction”, and can be investigated by measuring externalmagnetic field dependency of the resistance of the memory element andcomparing the direction of the magnetic field at this time between anin-plane direction and a perpendicular direction).

The reason why the magnetization of the Fe—Co alloy faces the directionperpendicular to the film face is considered to be because of acomposition in which the saturated magnetization amount Ms issignificantly smaller than the effective diamagnetic fieldM_(effective).

In addition, the reason why the thermal stability is secured even in thecase of the extremely minute element of a perpendicular magnetizationtype is related to Hk (effective anisotropy magnetic field) in theequation (2), and Hk of the perpendicular magnetization film becomes avalue significantly larger than that in the in-plane magnetization film.That is, in the perpendicular magnetization film, due to an effect oflarge Hk, it is possible to maintain a high thermal stability Δ even inthe case of the extremely minute element not capable of securing asufficient thermal stability Δ in the in-plane magnetization film.

From the above-described experiment results, in regard to the Co—Fealloy, in a case where the amount of Fe is 60% or more, this isappropriate to the ST-MRAM of Gbit class.

Experiment 4

In regard to the Co—Fe alloy expressed by a compositional formulaCO_(x)Fe_(100-x) in the above-described experiment 3, it can be seenthat in a case where the amount x of Co is 40% or less, this isappropriate to the ST-MRAM of Gbit class.

Therefore, in an experiment 4, B (boron) was added to the Co—Fe alloy toinvestigate an addition effect a heterogeneous element, and a memoryelement including the memory layer 17 having a composition(Co₃₀Fe₇₀)₉₂B₈ and the size of 50 nmφ was manufactured, and then thethermal stability was evaluated. The details of the sample other thanthe element size and the composition were substantially the same asthose in the experiment 1.

In regard to (Co₃₀Fe₇₀)₉₂B₈, a value of Δ that is an index of thethermal stability was 42. In addition, it was clear that themagnetization of the memory element faced a direction perpendicular tothe film face.

It was clear from the results that even when 8 atomic % of boron wasadded, the thermal stability was largely determined by the compositionof Co and Fe, and this was considered to be because an easy axis ofmagnetization was perpendicular to the film face.

Therefore, it was considered that the configuration where the thermalstability of the memory element was improved by adjusting thecomposition of the Co—Fe alloy to set the amount of Co to 40% or lesswas not hindered by the addition of the heterogeneous element. That is,an additive element such as boron may be added for the purpose ofgenerating a high tunnel magnetoresistive effect, for the purpose ofincreasing an insulating break-down voltage through the planarization ofan interface, or the like.

Hereinbefore, embodiments are described, but in the present application,the film configuration of the memory elements 3 and 53 illustrated ineach embodiments described above is not limited thereto, and variousfilm configuration may be adopted.

For example, in the embodiments, the magnetization-fixed layer 15 isformed of CoFeB, but the present application is not limited thereto andvarious configurations are possible without departing from the scope.

In addition, in the embodiments, a single underlying layer, a single capmaterial, and a single shape of the memory element are illustrated, butthe present application is not limited thereto, and variousconfigurations are possible without departing from the scope.

In addition, in the embodiments, the magnetization-fixed layer 15 isformed of a single layer, but a laminated ferri-pin structure includingtwo ferromagnetic layers and a non-magnetic layer may be used. Inaddition, the configuration may be a configuration where anantiferromagnetic film is applied to the laminated ferri-pin structurefilm.

In addition, the film configuration of the memory element may be aconfiguration where the memory layer is disposed at an upper side of themagnetization-fixed layer or at a lower side thereof, and in anydisposition, there is no problem at all. In addition, a structure wherethe magnetization-fixed layer is disposed at upper and lower sides ofthe memory layer, respectively, so-called a dual-structure has noproblem at all.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope and without diminishing itsintended advantages. It is therefore intended that such changes andmodifications be covered by the appended claims.

The application is claimed as follows:
 1. A memory element, comprising:a memory layer that maintains information through a magnetization stateof a magnetic material; a magnetization-fixed layer with a magnetizationthat is a reference of information stored in the memory layer; and anintermediate layer that is formed of a non-magnetic material and isprovided between the memory layer and the magnetization-fixed layer,wherein the storing of the information is performed by inverting themagnetization of the memory layer by using a spin torque magnetizationinversion that occurs according to a current flowing in a laminationdirection of a layered structure having the memory layer, theintermediate layer, and the magnetization-fixed layer, the memory layerincludes an alloy region containing cobalt (Co) and iron (Fe), and amagnitude of an effective diamagnetic field which the memory layerreceives during magnetization inversion thereof is smaller than ansaturated magnetization amount of the memory layer.
 2. The memoryelement according to claim 1, wherein a ferromagnetic material making upthe memory layer includes a Co—Fe alloy.
 3. The memory element accordingto claim 2, wherein the memory layer is formed of an alloy expressed byCo_(x)Fe_(100-x), and a direction of an easy axis of magnetization isperpendicular to a film face, here, x is atomic %, and 0≦x≦40.
 4. Thememory element according to claim 2, wherein the memory layer is formedof an alloy expressed by (Co_(x)Fe_(100-x))_(y)M_(1-y), and a directionof an easy axis of magnetization is perpendicular to a film face, here,M is an element other than Fe and Co, x and y are atomic %, 0≦x≦40,and0<y<100.
 5. A memory device, comprising: a memory element that maintainsinformation through a magnetization state of a magnetic material; andtwo kinds of interconnects that intersect each other, wherein the memoryelement includes a memory layer that maintains information through amagnetization state of a magnetic material, a magnetization-fixed layerwith magnetization that is a reference of information stored in thememory layer, and an intermediate layer that is formed of a non-magneticmaterial and is provided between the memory layer and themagnetization-fixed layer, the storing of the information is performedby inverting the magnetization of the memory layer by using a spintorque magnetization inversion that occurs according to a currentflowing in a lamination direction of a layered structure having thememory layer, the intermediate layer, and the magnetization-fixed layer,the memory layer includes an alloy region containing cobalt (Co) andiron (Fe), and a magnitude of an effective diamagnetic field which thememory layer receives during magnetization inversion thereof is smallerthan an saturated magnetization amount of the memory layer, the memoryelement is disposed between the two kinds of interconnects, and acurrent flows to the memory element in the lamination direction throughthe two kinds of interconnects, and according to this, spin torquemagnetization inversion occurs.
 6. The memory device according to claim5, wherein a ferromagnetic material making up the memory layer includesa Co—Fe alloy.
 7. The memory device according to claim 6, wherein thememory layer is formed of an alloy expressed by Co_(x)Fe_(100-x), and adirection of an easy axis of magnetization is perpendicular to a filmface, here, x is atomic %, and 0≦x≦40.
 8. The memory device according toclaim 6, wherein the memory layer is formed of an alloy expressed by(Co_(x)Fe_(100-x))_(y)M_(1-y), and a direction of an easy axis ofmagnetization is perpendicular to a film face, here, M is an elementother than Fe and Co, x and y are atomic %,0≦x≦40, and 0<y<100.